Not sure I understand your question. There are certain circuits that force the high idle in cold start, and one of the basic purposes of them is to heat the engine so that oil is warmed up and protects the engine. The fact that your tranny apparently only has its issue when the tranny is cold - before tranny fluid is warmed up and flowing more easily, might indicate that seals, etc., are brittle enough not to do their ‘job’ at cold start, before the tranny fluid is warmed up and flowing properly. You haven’t advised what kind of tranny fluid you are using - presumably it’s the correct one - but a bottle of AT-205 may give new life to you seals. Try it. You have little to lose.